Yacht Cradle with slings?

[Wishsong]

There used to be a company made a yacht cradle which had individual supports either side of the boat and a sling between them supporting the hull. I cannot find a trace of them the internet. Does anyone know if they still exist or have a contact name?

 

[2Tizwoz]

Do you mean like

this by any chance? /forums/images/graemlins/smile.gif

 

[Sinbad2222]

Good question. I have a lifting keel boat and would like to lower the keel for servicing and antifouling when the boat is out of the water. I think modern hulls are flimsy and would deform if supported in a few places by solid supports (ie without the keel being supported). A couple of webbing slings at the appropriate locations along the length of the hull would be ideal. I wonder if I could make such a cradle myself but that might be a bit risky!

 

[Wishsong]

Yes just like that. Is the company still around?
Have you actually used these, they don't look particularly stable?

 

[savageseadog]

It's called (or the company) the Sigma something or another, perhaps Holdfast.

Re Making a cradle for a lifting keel yacht, I've seen something made from a wood and steel frame with two pices of plywood cut to the hull shape made into a box section if you can understand what I mean.

 

[oldsaltoz]

G'day Sinbad,

We built one a few years ago:

Made with RSJ or 'I' beam, a simple rectangle base with capital 'H' at the front, the hull sits in the top of the 'H' with a carpet covered shaped timber on the horizontal of the 'H' and the top two uprights padded for the rubbing strake. This means you drive the boat on till the front is firmly in the 'H'.

The rear had a hinges arm on each side with a wide web lifting strap between them, this was fixed with chains near each end so that the sling could be adjusted and set the keel clearance.

Avasgoodweekend......

 

[Sinbad2222]

Oldsaltoz, thanks for that. I presume you welded the RSJs. Ideally I would like a transportable unit but nuts & bolts fixing together of the RSJs might involve more bracing for safety.

 

[Avocet]

Wouldn't the thing in the photo put a massive compressive load into the deck? It doesn't look like there is any other way of keeping the tops of the posts apart.

 

[Lakesailor]

If it's for a fin keeler, the weight will be on the ground and the posts will merely stop the boat starting to topple. The forces about the vertical position are very slight.

 

[oldsaltoz]

G'day Sinbad,
Yes it was welded but we could have bolted it together by adding plates with double nuts welded on the blind side, pretty simple setup, just ensure you have 4 bolts at each join and you should have no problems.

Avagoodweekend......

 

[rob2]

I built a cradle for my finkeeler out of scaffolding poles. The joints are like you see in the handrails in any municipal park (very neat). Overall cost around £300. I added heavy duty strops from a local supplier of lorry slings, 5 ton breaking strain. These are run under the hull between the uprights and along the length to pre-load the bracing. When the boat is in it she's far more rigidly held than the commercial produced cradle on my previous boat!

 

[chasroberts]

It looks like the legs need turning so that the support struts are facing inwards.

Or maybe I'm wrong....

 

[Wishsong]

I think the principle behind these is that the load is distributed across the hull by the slings rather than on four pads. If the ends of the slings are high enough up the hull the loads should be mainly vertical. There is bound to be some forces pulling the tops together but it won't be much, just enough to keep them in place.
I still can't find the company that makes them, I guess they must be defunct. (Or not on the net???)
I wouldn't recommend this as a system for a lifting keel as there is nothing to stop fore and aft movement other than the weight of the boat on the keel.
Turning the supports round would reduce your base width and make it more likely to tip in a side wind.
Think I might make some, possibly with a triangulated base. I'll post the drawings if they work. Does anyone know what the optimum angle for the prop is? 25 degrees?

 

[Avocet]

I can't help feeling that if I sat on one of the slings, I'd get pinched very hard between the tops of the posts! I agree that for a fixed keel boat, the compressive loads wouldn't be to bad but for a lif-keeler I really wouldn't fancy it!